Let me see if I can make this explainable. Please bare with me.

Okay. I have air coming out of just the A/C vents.
With the A/C off. At first the air would slightly come from the front vents when taking off and quit once you got to a set speed. If you punched the gas it would blow air but then go away once again after speed was set.
Now when you drive 10,20,30mph etc. It blows out as if it's on like the 2 setting. It does not go away once speed is set.
I use to be able to use Defrost or floor or mix,etc. Now the only one that works is the a/c vents.
I checked the hoses and no leaks. I cannot find that vaccum ball everyone tells me about.

P.S. I took the glove box down to check the hoses and when I move the selector switch from say floor to defrost nothing in there moves.

Any help will be deeply appreciated.

 

It sounds like a blend door actuator. This is a pretty old post, I'm curious if you have been succesful at finding the problem.

 

Are you sure you have a vacuum supply to control switch and that it is working.

 

I've attached a file with location of HVAC vacuum storage on 98 S-10.

It appears the vacuum lines in this area (near ABS plumbing on 2004 S-10) could be easily damaged ... have you checked the lines?